Method for cooling a tuyere of a refining converter

ABSTRACT

A METHOD FOR COOLING THE TIP OF A TUYERE USED FOR INTRODUCING AN OXIDIZING GAS INTO A MOLTEN METAL BATH OF A BOTTOM-BLOWN REFINING CONVERTER. THE METHOD COMPRISES INJECTING A COOLING AGENT INTO THE CONVERTER PERIPHERALLY OF THE TUYERE, WHERE THE COOLING AGENT IS A LIQUID UP TO THE TIP OF THE TUYERE.

June 18, 1974 .5, LERQ ETAL 3,817,744

METHOD FOR COOLING A TUYERE OF A REFINING CQNVERTER Original Filed June 29, 1970 Q 2 Sheets-Sheet 1 June 18 1974 p, ER EIAL 3,817,744

METHOD FOR COOLING A TUYERE OF A REFINING CONVERTER Original Filed June 29, 1970 2 Sheets-Sheet 2 //i A N United States Patent C) 3,817,744 METHOD FOR COOLING A TUYERE OF A REFINING CONVERTER Pierre Leroy, St. Germaiu-en-Laye, Marcel Gombert, Metz Queleu, and Emile Sprunck, Moyeuvre-Grande, France, assignors to Creusot-Loire, Societe Anonyme, Paris, and Weudel-Sidelor, Hayange, France Continuation of abandoned application Ser. No. 50,393, June 29, 1970. This application Aug. 14, 1972, Ser. No. 280,203 Claims priority, application France, July 8, 1969, 6923145; Nov. 13, 1969, 6938923; June 23, 1970,

Int. Cl. C21c 5/34 US. Cl. 75-60 16 Claims ABSTRACT OF THE DISCLOSURE A method for cooling the tip of a tuyere used for introducing an oxidizing gas into a molten metal bath of a bottom-blown refining converter. The method comprises injecting a cooling agent into the converter peripherally of the tuyere, where the cooling agent is a liquid up to the tip of the tuyere.

CROSS REFERENCE TO RELATED APPLICATIONS This is a continuation of U.S. application Ser. No. 50,393, filed June 29, 1970, now abandoned.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to improvements in the methods of cooling the tuyere of a refining converter, more particularly of a submerged tuyere blowing in an upward direction, ether vertically or obliquely.

Description of the prior art Since the invention by Henry Bessemer in 1856 of the first autogeneous process for refining iron into steel, the desirability of using pure oxygen to oxidize the impurities in molten iron has been recognized. Among the advantages of pure oxygen over the atmospheric air blast traditionally used in the Bessemer process are (i) decreased blowing time because all of the oxidizing gas is reactive and thus increased production; (ii) a more favorable heat balance and thus the ability to melt more scrap; and (iii) decreased nitrogen content in the finished steel.

The Bessemer process has been in wide use, particularly in Europe, for over a century. It consists of blowing a blast of atmospheric air through a large number of holes (tuyeres) formed in the refractory substance comprising the bottom of an open-mouthed, cylindrical vessel containing a charge of molten iron to be refined. Steelmakers sought to enrich the blast with pure oxygen but soon found that when the oxygen content of the blast exceeded about 40 percent, the refractory bottom, particularly in the zones around the tuyeres, was rapidly consumed. Attempts at blowing pure oxygen were met with bottom failure, usually before one heat was completed. The cause of this high wear rate is believed to be a combination of localized high temperatures generated from the reaction of oxygen with the molten iron and the corrosive effect of the ferrous oxide produced by that reaction.

The early efforts of workers in the art to cure the problem of rapid deterioration of the converter bottom by cooling the tuyeres during oxygen blowing produced no commercially practical results: Lellep US. Pat. No. 2,333,654 discloses cooling the tuyeres in a converter bottom by circulating water in an annular duct surrounding the oxygen supply pipe but without the water contacting the hot metal. Lellep also provides a thin refractory 3,817,744 Patented June 18, 1974 lining on the bottom with water circulating in a closed passageway beneath the bottom. The danger of explosion associated with the presence of water in proximity to molten iron appears to have discouraged steel makers from adopting Lelleps teaching. Kosmider et al. US. No. 2,829,879 teaches the use of copper tubes to form the tuyeres in a converter bottom instead of employing conventional tuyeres formed directly in the converter bottom. This arrangement relied upon the high heat conductivity of copper to effect cooling of the tuyere. Variations of the Kosmider et al. concept are disclosed in Savard et al. US. Pat. No. 2,855,293 and Compagnie Des Ateliers et Forges de la Loire French Pat. No. 1,503,756. The more recent attempts to overcome erosion of the tuyere zones in a converter bottom-blown with oxygen involve the use of a double tuyere. This is an arrangement of two concentric pipes located in the converter bottom; oxidizing gas is blown into the bath through the central pipe and a gas which endothermically dissociates upon striking the molten metal is blown through the annular space formed between the inner and outer pipes. Examples of the gases blown through the annulus to shield the oxygen jet are steam or carbon dioxide (Westfalenhuette French Pat. No. 1,058,181; The Application of Oxygen in the Production of Steel, edited by I. P. Bardin and published by VEB Verlag Tecnik Berlin in 1959, p. 221; and Centre National de Recherches Metallurgiques Luxemburg Pat. No. 41,718); gaseous hydrocarbons (LAir Liquide French Pat. No. 1,450,718); and inert gas or vapor (Holmes et al. US. Pat. No. 3,397,878).

Concomitant with the attempts to arrest rapid consumption of the tuyeres by use of the double tuyere and blowing gas or vapor around the oxygen jet were the efforts of other workers to achieve reduced erosion in the tuyere zone by introducing a coolant into a sheath of porous refractory surrounding a central oxygen duct. In at least one instance, the purpose of this arrangement is to form a protective layer of gas bubbles at the interface of the refractory sheath and the molten metal to inhibit erosion of the refractory which is taught to occur in an annular zone around the outlet of the oxygen duct. Examples of this technique and its accompanying devices are found in De 'Moustier et al. US. Pat. No. 3,330,645 and Lutgen US. Pat. No. 3,490,755; but no commercial significance can be attached to their teachings.

In summary, therefore, all known attempts to reduce rapid deterioration of the refractory bottom and tuyere caused by oxygen issuing from a tuyere located at a converter bottom have uniformly involved the use of a gas or vapor as a coolant.

'Ihe conditioning of cooling gases is attended by certain problems. For example, expensive equipment is required to store gas and deliver it to its point of use at the required conditions of temperature and pressure. Elaborate safety precautions must be observed to guarantee safe handling of gas under pressure and these measures become more diflicult to maintain in the environment of a steel plant. In the case of steam, super heating apparatus may be required and special precautions must be taken to prevent condensation. In general, the benefits derived from use of the processes employing gaseous cooling agents have not justified the expense and/or precautions required for their utilization.

Moreover, the cooling eflect of a gas or vapor is limited to (i) the sensitive heat absorbed by the gas in heating it and (ii) the heat absorbed in the thermal dissociation of the gaseous molecules.

SUMMARY OF THE INVENTION It is the primary object of this invention to overcome the shortcomings of the prior art processes by markedly improving the cooling of the tip of the tuyere through the use of a liquid cooling agent. This marked improvement is effected by taking advantage of the heat required to elevate the temperature of the liquid and vaporize it (heat of vaporization). At the same time, the invention permits a reduction in the amount of cooling agent required over the prior art processes employing gas.

To this end the present invention provides a method of cooling the tuyere of a refining converter which comprises a double, separate feed system, characterized in that a cooling liquid such as water under pressure, liquid carbon dioxide or a hydrocarbon containing liquid is injected into the peripheral circuit.

According to a specific feature of this invention, the cooling liquid is introduced into a gap formed between two concentric tubular ducts, this gap being of annular or other configuration.

If water under pressure is used as a cooling medium it is introduced into the peripheral circuit of each tuyere, possibly after preheating for example at 80 C. (176 F.).

According to this invention, in order to obtain a cooling liquid circulation rate high enough to cause the vaporization to take place at the tip of the tuyere, it is contemplated to use an oxygen delivery duct having a cross-sectional passage area at least 30 times greater than that of the liquid passage duct in each tuyere.

According to the method of this invention, to avoid the introduction of liquid coolant into the converter, since this would cause an immediate vaporization of this coolant, the initial part of the blowing process is performed by introducing the oxidizing gas, for example pure oxygen, into the peripheral circuit and at the same time into the axial circuit, and after the beginning of the metal melt refining process, by producing a switching or reversal whereby the selected liquid under pressure is substituted for the oxidizing gas in the peripheral circuit alone.

According to a specific feature characterizing this invention, the pressure and temperature of the carbon dioxide used as cooling agent are in all cases selected with a view to keep the product in the liquid state until it penetrates into the tuyere, the pressure and temperature being advantageously of 5 to 25 bars (72 to 365 psi.) and 45 to l3 C. (49 to 8.6 F.) respectively, in which case the density of liquid carbon dioxide differs but slightly from that of water.

Accordingly to another specific feature of this invention, there are utilized in succession, as cooling agent, firstly water and then liquid carbon dioxide, or conversely, firstly liquid carbon dioxide and then water, in a same set of tuyeres.

According to another feature characterizing this invention, which is advantageous notably in the production of low-hydrogen steel grades, the first part of the conversion is carried out by using water as a tuyere cooling agent, and the second part of the conversion is carried out by using liquid carbon dioxide as a cooling agent. Thus, the stirring of the metal melt by the carbon monoxide resulting from the decomposition of the carbon dioxide permits the release of the hydrogen contained in the melt before the conversion process is completed.

The chief advantage resulting from the use of liquid carbon dioxide, in comparison with the use of water, is that very low hydrogen contents can be obtained in the steel, and in comparison with the use of carbon dioxide gas, that the undesired preliminary evaporation can be avoided, as this evaporation requires the use of a special, cumbersome equipment, while taking advantage of the improved cooling capacity per weight unit of liquid carbon dioxide utilized, since a cooler product is used, the vaporization of which will absorb additional heat from the tip of the tuyere.

Another advantage is that it is relatively easy to switch from water to liquid carbon dioxide, or vice-verse, in a same set of tuyeres, since both liquids have approximately the same density.

However, particular care must be exerted throughout the circuit for avoiding local expansions of the liquid carbon dioxide which might cause the formation of carbonic acid snow likely to clog the circuit.

By using according to this invention a hydrocarbon containing liquid as a coolant a still better cooling effect at the tip of the tuyere is obtained by taking advantage, furthermore, of the heat released by the dissolution of carbon in molten steel, but still without resorting to a gaseous cooling agent.

According to this invention, a hydrocarbon-containing cooling liquid may be fuel-oil whether of domestic grade, or light fuel-oil, or heavy oil, or naphtha.

According to a specific feature characterizing this invention, the hydrocarbon containing cooling liquid is a mixture of water and fuel-oil, or water and naphtha, this mixture being used if desired in the emulsion form.

According to a further feature characterizing the pres ent invention, which is particularly advantageous for producing low-hydrogen steel grades, the first part of the conversion process is carried out by utilizing a hydrocarbon-containing liquid as a cooling agent and the second part by utilizing liquid or gaseous carbon dioxide.

Another feature characterizing this invention consists of introducing a scavenging gaseous stream consisting of atmospheric air or neutral gas into the tuyere when the supply of oxidizing gas blown through the axial circuit, or the supply of cooling liquid is discontinued.

According to a complementary feature characterizing this invention, the desired cooling liquid output is adjusted by using means such as volumetric pumps for introducing this cooling liquid, by varying the pump pressure irrespective of the possible variations in the crosssectional passage area available for the liquid at the tip of the tuyere, as a consequence for example of partial clogging due to metal having set therein, and followed by a partial or complete remelting of the deposits thus formed.

The process of the invention with a device comprising two concentric tubes and being characterized in that those tubes are selected to have very close diameters and are positioned in mutual telescopic or sliding engagement. Rectilinear splines or grooves are provided at the limit of the two concentric tubes, such splines or grooves being used for introducing the cooling liquid. These splines may be machined on the outer face of the inner tube, the latter being slidably mounted in another tube with a very small clearance therebetween and these splines may extend transversely and have a circular or semi-circular cross-section, or constituted circular segments.

According to a modified embodiment, the device comprises, for introducing the cooling liquid, a number of helical splines or grooves formed at the limit of a pair of concentric tubes having very close diameters and slidably engaging each other. These helical splines or grooves are machined preferably on the outer face of the inner tube, the latter sliding in the other tube with a relatively small clearance.

BRIEF DESCRIPTION OF THE DRAWINGS Other features and advantages of this invention will appear as the following description proceeds with reference to the attached drawing illustrating diagrammatically by way of example various forms of embodiment of the invention; in the drawing:

FIGS. 1 and 2 are a vertical axial section and a horizontal cross-section, respectively, of a first embodiment of a device illustrating the use of the process of the present invention, and

FIGS. 3 and 4 are similar views showing another embodiment of a device illustrating the use of the process of the present invention.

5 DESCRIPTION OF THE PREFERRED EMBODIMENTS In the first embodiment (FIGS. 1 and 2) of a device for carrying out the process of the invention applicable to a tuyere of relatively small diameter the device comprises, for blowing pure oxygen, a copper tube '10 having an inner diameter of for instance 3 mm. and an outer diameter of for instance 6 mm., sliding with a very moderate play in an outer metal tube 12 having an outer diameter of for instance 8 mm. and an inner diameter of for instance 6 mm. On the outer face of the inner tube 10 eight rectilinear splines or grooves 14 having a radius of for instance 0.3 mm. are machined at angular intervals of 45 from one another, their cross-sectional contour being substantially semi-cylindrical. If water under pressure is used as a cooling agent, a suitable output is obtained for an output of 300 to 400 liters per minute and a 12"-long tuyere.

In the second embodiment of a device for carrying out the process of the invention (FIGS. 3 and 4) the tuyere has a larger diameter and comprises for blowing oxygen a copper tube 16 centered at spaced points in an outer tube 18. The annular space 20 is such that the cooling liquid output (water under pressure) is adequate, in this example, for an oxygen output of 7 to 10 Nmfi/min.

This method is attended notably by the following advantages:

low cost of the cooling agent;

the conditioning of the liquid cooling agent is easier than that of gaseous agents;

high pressures can be obtained and distributed with greater ease.

However, cooling according to the method of this invention by using a hydrocarbon-containing liquid is attended by the following advantages in comparison with water cooling: the cooling effect resulting from the vaporization heat, the heating due to overheating, and the dissociation heat, is completed by the effect resulting from the heat released as a consequence of the carbon dissolved in the metal melt, and'thus leads to a lower consumption of hydrocarbon-containing cooling liquid than if water alone were used, or alternatively to an improved cooling eifect at the tip of the tuyere.

Two other modifications of the method of this invention will be described by Way of example, not of limitation:

The first relates to the cooling of tuyeres by using domestic fuel-oil having a density of 0.84.

The second relates to the cooling of tuyeres by using a mixture of water and domestic fuel-oil, in the proportion of 50/50.

During the following description reference will be made to FIGS. 1 and 2 illustrating the above-described tuyere which, except for the dimensions, may be used in the examples described hereinafter.

This tuyere comprises, for blowing pure oxygen, a copper tube 10 having an inner diameter of 11 mm. and an outer diameter of 14 mm., which slides with a very small clearance in an outer metal tub e 12 having an inner diameter of 14 mm. and an outer diameter of 16 mm. On the outer surface of the copper tube there are machined eight rectilinear splines or grooves 14 of crescent-shaped or semi-circular*"cross-sectional contour, which are disposed at spaced ihtervals, therefore at 45 from each other, around the tube periphery.

In these two examples, the eight rectilinear splines or grooves of crescent-shaped cross-sectional contour have a cross-sectional passage area permitting the flow of a cooling fluid output adequate for accompanying an oxygen output of the order of Nmfi/min. in the central tube under an upstream pressure of about bars (145 p.s.i.).

However, in the second example with a cooling fluid consisting of a mixture of water and domestic fuel oil, the total cross-sectional passage area of the splines or grooves 14 (and therefore the radius of each spline or groove) is greater than that of the first example, wherein the cooling fluid is only consisting of domestic fuel-oil.

In all cases, before converting the metal to be refined a suitable scavenging gas is blown through the circuit consisting of said splines or grooves 14 and also through the central tube 10 in order to protect the tip of those splines and also of the central tube against any clogging by a foreign substance from within the converter, however without allowing cooling liquid to flow into the converter in the horizontal inoperative position.

Then, when the metal to be refined is present in the bottom of the converter, there is effected a switching which consists in substituting pure oxygen for the scavenging gas in the central tube 10, and fuel-oil or a water and fuel-oil mixture for the scavenging gas in the circuit comprising the splines 14. Then the converter is raised to its vertical position for performing the blowing process according to the method of this invention.

At the end of the conversion process the reverse operation is performed, i.e., after having inclined or dumped the converter, on the one hand scavenging gas is substituted for the oxygen in the central tube and on the other hand scavenging gas is substituted for the fuel-oil or water and fuel-oil mixture in the splines.

By adhering to this procedure any risk of pouring fueloil or water into the empty converter, just before the charging of same with molten metal to be refined, which would cause strong projections, is safely eliminated.

Of course, this invention should not be construed as being limited by the specific embodiments described and illustrated herein, and by the details thereof given by way of example, since many modifications and variations may be brought thereto without departing from the basic principles of the invention as set forth in the appended claims.

What is claimed is:

1. A method for cooling the tip of a tuyere submerged in a refining converter, said tuyere being used for introducing an oxidizing gas into a bath of molten metal in said converter, said method comprising:

injecting a cooling agent into said converter peripherally of said tuyere, said cooling agent being in the liquid state up to the tip of said tuyere.

2. A method as recited in claim 1 wherein: said cooling agent is injected peripherally of said tuyere tip.

3. A method as recited in claim 1 wherein: said oxidizing gas is oxygen.

4. A method as recited in claim 3 wherein: said cooling agent is selected from at least one of the group con sisting of water, carbon dioxide in the liquid state and a liquid hydrocarbon.

5. A method as recited in claim 1 wherein: said cooling agent is injected in the liquid state into a gap formed by said tuyere and a tube concentrically surrounding said tuyere.

6. A method as recited in claim 5 wherein: said oxidizing gas is oxygen.

7. A method as recited in claim 6 wherein: said cooling agent is preheated. water injected under pressure.

8. A method as recited in claim 6 wherein: said cooling agent is liquid carbon dioxide.

9, A method as recited in claim 8 wherein: said liquid carbon dioxide is injected at a pressure in the range of 5 to 25 bars and at a temperature in the range of 45 C. to 13 C.

10. A method as recited in claim 6 wherein: said cooling agent is a hydrocarbon-containing liquid.

11. A method as recited in claim 10 wherein: said bydrocarbon-containing liquid is fuel oil.

12. A method as recited in claim 10 wherein: said hydrocarbon-containing liquid is naphtha.

13. A method as recited in claim 6 wherein: said cooling agent consists of a mixture of water and hydrocarboncontaining liquid in emulsion form.

14. A method as recited in claim 6 wherein:v a predetermined amount of cooling agent injected into the converter is maintained by varying the pressure of injection in accordance with variations in said gap due to partial clogging thereof by metal having solidified therein.

15. In a process for refining iron in a converter to produce steel having low hydrogen content, the method of cooling the tip of a tuyere submerged in said converter, said tuyere being used for introducing an oxidizing gas into said converter, said method comprising: injecting a first cooling agent into said converter peripherally of said tuyere during a first period of said refining process, said first cooling agent being water in the liquid state up to the tip of said tuyere, and injecting a second cooling agent into said converter peripherally of said tuyere during a second period of said refining operation, said second cooling agent being carbon dioxide in the liquid state up to the tip of said tuyere.

16. In a process for refining iron in a converter to produce steel having low hydrogen content, the method of cooling the tip of a tuyere submerged in said converter,

v v ReferencesCited UNITED STATES PATENTS r 3,706,549 12/1972 Krmppel '75 3,330,645 7/1967 De Moustiere -40 FOREIGN PATENTS 585,737 1/1960 Belgium '75--60 L. DEWAYNE RUTLEDGE, Primary Examiner P. 1). ROSENBERG, Assistant Examiner. 

